1. Field of the Invention
Rotary force transfer devices: clutches, couplings and the like, play a major roll in our mechanized society. They are found in machinery of all levels of complexity from fishing reels to helicopter rotors and with applications which vary from door opening devices to space flight.
This invention relates to rotary force transfer couplings. More particularly, the present invention relates to such a coupling wherein the output member is enabled to free wheel relative to the input member when the input member is stopped and wherein, further, the output member is precluded from transmitting a rotary backdriving force to the input member. A Tether Return Unit utilizing this invention is useful in manned spaceflight.
During extravehicular activity by astronauts in space flight it is sometimes necessary to utilize a tether by which the astronaut is secured to the spacecraft in order to prevent too great a separation from it and which further provides a backup means for returning to the spacecraft should the astronaut's powered maneuvering unit malfunction for any reason. If a crank and reel arrangement attached to the astronaut's person is used to effect the return, it is desirable that it be of such nature that when the astronaut is moving away from the spacecraft under power (by use of a powered maneuvering unit, for example), powered rotation of the crank will be prevented so as not to injure the astronaut or cause damage to the spacesuit. It is also a desirable feature of the crank and reel arrangement that if the crank is turned backward the reel becomes disengaged so as not to uncontrollably unwind the line from the reel and thereby tangle the line.
2. Background Art
As used in this invention the term "backdriveable" means that the output member is capable of driving the input member and "non-backdriveable" means the output member is incapable of driving the input member. The term "freewheeling" means that the output member continues to turn when the input member is stopped; or that the output member can turn faster than the input member. Free wheeling couplings including input and output members and axially shifting coupling members and having clutch teeth moveable between engaged and disengaged positions as a result of the axial motions of the coupling member are known. For example, U.S. Pat. No. 3,721,325 to Richmond discloses a non-backdriveable coupling which uses a ratchet and pawl mechanism working between the coupling member and the output member and controlling the movement of the coupling member to effect engagement and disengagement of the clutch teeth. In its free wheeling mode the ratchet overruns the pawl. U.S. Pat. No. 2,061,220 to Cotterman, U.S. Pat. No. 479,192 to Leedle, U.S. Pat. No. 1,597,198 to Howell, U.S. Pat. No. 599,321 to Doremus, and U.S. Pat. No. 627,876 to Price are free wheeling clutches which differ from this invention in that they are inherently backdriveable. U.S. Pat. No. 1,098,189 to Stocker is a free wheeling clutch which differs from the present invention in that it utilizes a shifting lever to effect engagement and disengagement. None of the art discussed above teaches a non-backdriveable coupling which is also free wheeling and which, additionally, positively disengages input and output members thus eliminating continuous or intermittent drag in the free wheeling mode.